This invention relates to novel compositions including, in one aspect, novel compositions useful as separations media.
Separations media for separation process applications, including separations column packing materials for reverse phase chromatography columns, can be supplied from organic resins. However, these organic resin packing materials have certain drawbacks including poor physical strength, poor thermal stability, high cost, solvent swelling, and low capacity.
Separations media including chromatographic packing materials made from metal oxides overcome some of the problems related to organic resins but have some problems of their own. For example, silica-based separations column packing materials exhibit poor chemical stability at high pH values. Although silica-based separation materials are dominant in the marketplace for reverse phase column packings, silica-based separation materials have shortcomings of a relatively narrow operating pH range, e.g., such as about 2-8, and a high pressure drop requirement through the separations column. The narrow operating pH range of silica-based separation materials usually results in shorter column life, loss of separations versatility, and difficulty in the cleanup with strong alkali and acid for cost effective, high speed analytical, semi-preparative and preparative purification of samples. A high pressure drop of the silica-based materials also limits the ultimate speed and separation capabilities of the chromatography column.
Metal oxides such as alumina have been used as adsorbents because of good physical integrity and low cost. Aluminas have been used frequently as separations media, including separations media in classical adsorption chromatography. However, the use of aluminas as separations media for modern high performance liquid chromatography in the reverse phase has not been as successful as silica. Reverse phase chromatography involves adsorption on an adsorbent less polar than the eluting solvent. Contrastingly, normal phase chromatography involves an adsorbent more polar than the eluting solvent. In reverse phase chromatography, the more non-polar sample components interact more with the relatively non-polar column packing and thus elute later than polar sample components. The diminished use of aluminas as separations media in high performance chromatography in the reverse phase is because alumina is not easily converted to a hydrophobic phase for selective chromatographic separations via chemical bonding the surface by various hydrocarbon groups, e.g., alkyl or phenyl. Most silanization reagents used successfully with silica show no reactivity toward aluminas. Although chlorosilanes react with alumina, the formed Al(--O--Si--C) bond is known to be highly unstable under reverse phase chromatographic conditions.
U.S. Pat. No. 4,045,353 discloses that the prior art suggests solid supports having cores coated with a porous silica surface and solid supports coated or chemically bonded with an organic compound or organic polymer gel have been used to meet the requirements of high speed liquid chromatography. The patent discloses a solid support prepared by immersing an inorganic substrate in a radiation-polymerizable monomer. Suitable polymerizable monomers include the ethylenically unsaturated monomers, e.g., such as styrene monomer, fluorine monomer, silicon-containing monomer, acrylates, methacrylates, vinyl monomer, olefin monomers, diene monomers, e.g., such as butadiene, isoprene, 1,3-pentadiene, cyclopentadiene, chloroprene, or other monomers capable of being radiation polymerized such as the aldehydes, ketones, cyclic ethers, or the like. Such a polymer can be grafted (the patent discloses) on a substrate of "silica, silica gel, alumina, diatomaceous earth, zeolite, porous glass, carbon black, active carbon, clay, etc."
It is an object of the present invention to provide novel materials useful as separations media in a packed bed.
It is another object of the present invention to provide a novel composition useful as a reverse phase chromatographic column packing material.
It is a further object of the present invention to provide a reverse phase chromatographic column packing material which overcomes the problems of prior art column packing materials.
These and other objects of the present invention will become apparent from the detailed description which follows.